The operator has initiated a cyclic-steam-stimulation (CSS) project in the Opal A diatomite of the Sisquoc formation on the Careaga lease in the Orcutt oil field in Santa Barbara County, California. The operator has received entitlement to proceed with an expansion consisting of 110 additional new wells. This paper discusses steam-injection step-rate tests (SRTs) for this asset.
The target zone contains high oil content ranging from 1,800 to 3,000 bbl/acre-ft in massive intervals with 200- to 700‑ft thickness at depths of 600 to 1,000 ft and with a permeability of 5 to 15 md. The pilot currently consists of 19 cyclic-steam-injection wells configured in a 4×5 matrix spaced approximately 120 ft apart, producing from an average depth of 925 ft.
A supervisory control and data-acquisition system is used to control and monitor various aspects of field operations, especially the steam-injection-process protocols. Relatively low steam-injection rates of 250 to 450 B/D cold-water equivalent are used with 70% constant-quality steam. Steam-injection pressures and rates have been monitored closely throughout the process since startup in October 2009.
More than 1,000 steam-injection cycles have been completed as of this paper’s writing. For all cycles, the onset of formation parting has been detected less than 0.5% of the time. In all detected events, steam injection was adjusted or halted without loss of steam-injection containment. Steam injection was resumed when it was determined to be safe to do so, and matrix flow was re-established. To this end, two operational procedures exist for analyzing data as part of the operator’s efforts to improve steam-injection practices further and to improve understanding of the mechanisms leading to oil production. One is taken from common waterflood surveillance practices and graphically displays changes in flow resistance during injection, aimed at indicating if formation parting or a loss of steam confinement is initiating. The other is analysis of the pressure falloff observed during the soak period between injection and production, a period intended to allow pressures and temperatures to dissipate away from the vicinity of the well and into the producing zone.
Case Study: Steam-Injection Step-Rate Tests Run in the Orcutt Oil Field
10 May 2016